The present invention relates to aqueous cleaning compositions in which the pH can be adjusted to provide efficient cleaning and unique safety for the user and the surface to be treated.
Cleaning of industrial machinery and equipment, such as metal coils, can present problems because of the many different materials used to make such equipment. Any cleaning composition used must therefore not only clean properly, but must also avoid causing damage to the various components and to the various materials in the components of the equipment.
Several cleaning compositions have been formulated for use in cleaning various metals. Unfortunately, many cleaners that have been found to be good at brightening and removing soil have also been linked to problems with damaged surfaces, particular with cleaning coils. However, none of these compositions provides for an adjustable pH to provide efficient cleaning and safety to the user as well as to the materials cleaned.
Garabadian et al., in U.S. Pat. No. 5,252,245, disclose an aqueous cleaner for hard surfaces such as glass windows comprising an alkanol solvent, a surfactant, and a buffering system. In this case the buffer is used to reduce streaking and filming of hard surfaces.
Howe et al., in U.S. Pat. No. 5,556,833, disclose an aqueous cleaning composition for cleaning soils from surfaces of painted steel and the like. This cleaning composition comprises at least one acid fluoride salt such as ammonium bifluoride, a nonionic surfactant, and a terpene. The pH of the composition is from about 3.0 to 6.5, but there is no provision for adjusting the pH of the composition.
Fidgore et al., in U.S. Pat. No. 6,001,793, disclose a cleaning composition comprising at least one terpene solvent, a nonionic surfactant, and an anti-corrosion agent such as triethanolamine. The pH of this composition is preferably less than about 9.5.
It is an object of the present invention to overcome deficiencies in the prior art.
It is another object of the present invention to provide an aqueous cleaning composition that has a pH which can be adjusted to between about 3.5 and 7.0.
It is a further object of the present invention to provide an aqueous cleaning composition which is particularly useful in cleaning metals and combinations of metals and non-metals with minimal corrosion effects, particularly on aluminium.
According to the present invention, an aqueous cleaning composition is provided based upon an acidic metal salt such as ammonium bifluoride in which the pH of the composition can be controlled by addition of a nitrogen compound such as an ethanolamine, EDTA, or NTA. By adding such a nitrogen compound, one can adjust the pH of the composition to be best suited to the substrate to be cleaned.
More particularly, the aqueous cleaning compositions of the present invention include water, an acidic metal cleaning compound, at least one nitrogen containing compound, a nonionic surfactant, and an emulsifying agent. Additional water soluble solvents which have a vapor pressure of less than about 4 mmHg at 20xc2x0 C. may optionally be included. A typical formulation can include ammonium bifluoride, a terpene emulsifying agent, an alkyl phenol nonionic surfactant, an alkanolamide an an alkanolamine for pH stabilization.
The aqueous cleaning composition of the present invention is particularly well suited for cleaning cooling coils, but is not limited thereto. Cooling coils must be cleaned periodically to remove deposits which can build up on the surface of the coils and interfere with proper system operations. The pH of the cleaning composition of the present invention can be adjusted as needed.
The compositions of the present invention remove dirt and other deposits from metal surfaces, particularly from cooling coils. These compositions effectively clean and deodorize surfaces such as evaporator coils, condenser coils, window units, air filters, blowers, and other dirty HVAC surfaces, as well as any other type of metal or non-metal equipment. Because the cleaning compositions of the present invention contain no free acid, they will not etch metals such as aluminum. This is particularly important in cleaning evaporator coils because, if the metal surfaces of evaporator coils are etched, there may be water blow off on the evaporator coil, which in turn can cause microbial contamination downstream.
The primary active ingredient in the aqueous cleaning composition of the present invention is an acidic metal cleaning compound. While ammonium bifluoride is the preferred acidic metal cleaning compound for use in cleaning compositions according to the present invention, other fluoride salts can be used in the compositions. Other metal salts that can be used include alkali metal fluorides and ammonium fluorides. Specific fluoride salts include potassium bifluoride, sodium bifluoride, ammonium fluorides, calcium fluorophosphates, sodium fluorosilicates, and the like. These compounds are used in amounts ranging from about 0.1% to about 10% by weight.
The preferred solvent is a nonionic surfactant such as a nonylphenol polyglycol ether. However, other suitable nonionic surfactants can be used, including other ethoxylated alcohols such as condensation products of ethylene oxide with an organic compound containing an active hydrogen bound to oxygen or nitrogen atoms. Suitable nonionic surfactants include, but are not limited to, alkoxylated compounds produced by condensing alkylene oxide groups (which are hydrophilic in nature) with an organic hydrophobic compound, which may be aliphatic, aromatic, or aryl aromatic. Non-limiting examples of suitable nonionic surfactants also include polyethylene oxide condensates of alkyl phenols, i.e., condensation products of alkyl phenols having an alkyl group containing from 6 to 12 carbon atoms in either a branched chain or a straight chain configuration, with ethylene oxide being present in amounts equal to about 5 to about 25 moles of ethylene oxide per mole of alkyl phenol. The alkyl substituent in such compounds may be derived, for example, from polymerized propylene, diisobutylene, octene, and nonene. Other examples include dodecylphenol condensed with 12 moles of ethylene oxide per mole of phenol; dinonylphenol condensed with 15 moles of ethylene oxide per mole of phenol; nonylphenyl and di-iso-isooctylphenol condensed with 15 moles of ethylene oxide.
Further examples of suitable nonionic surfactants are the condensation products of primary or secondary aliphatic alcohols having from 8 to 24 carbon atoms, in straight chain or branched chain configuration, with about 1 to about 30 moles of alkylene oxide per mole of alcohol. Preferably, the aliphatic alcohol comprises between about 9 and about 15 carbon atoms and is ethoxylated with between about 2 and about 23, preferably between 3 and 9, moles of ethylene oxide per mole of aliphatic alcohol.
Other nonionic compounds that can be used in the present invention can be prepared by condensing ethylene oxide with a hydrophobic base formed by the condensation of propylene oxide with either propylene glycol or ethylene diamine.
Other suitable solvents include tripropylenemethyl ether (TPM), gamma butyrolactone (GBL), and pyrrolidones such as N-methyol-2-pyrrolidone.
The preferred nitrogen containing compounds for use in compositions of the present invention are alkanolamides, such as coconut diethanolamide, modified. Other suitable alkanolamides include lauric/myristic monoethanolamide, coconut monoethanolamide, lauric diethanolamide, unmodified coconut diethanolamide, and other modified fatty alkanolamides. Other suitable nitrogen containing compounds that fit the chemical vapor pressure profile are pyrrolidones such as N-methyl-2-pyrrolidone (NMP). These compounds increase the cleaning ability of the compositions and increase the viscosity of the compositions, which includes the xe2x80x9ccling timexe2x80x9d to the substrate being cleaned.
Other nitrogen containing compounds that can be used in the compositions of the present invention included di-tri, and tetra sodium salts of ethylene diamine tetra acetic acid. Furthermore, modified imidazole derivatives such as sodium cocoamphoacetate can be used.
An emulsifier can be used to ensure that the compositions remain clear upon dilution. A preferred emulsifier is a terpene emulsifying agent.
The pH of the compositions is adjusted to the desired level between about 3.5 and about 7.0 by adding at least one nitrogen containing compound. Alkanolamines such as triethanolamine can be used, particularly short chain, e.g., C1-C6 alkanolamines such as mono-, di- and triethanolamines, which may be used alone or in admixture with each other or with other alkanolamines. Other such compounds for pH adjustment include compounds such as di-, tri-, and tetra sodium salts of ethylene diamine triacetic acid (EDTA) and nitrilotriacetic acid (NTA), alone or in combination with alkanolamides of C1-C6 alcohols and modified imidazoline derivatives.
The following examples are provided to illustrate the present invention, but are in no way intended to limit the invention.
Several 200 gram batches of cleaning solutions were prepared, and their cleaning efficacies were tested, with 5 being excellent, 1 being poor.
It was found, however, that the following formulation provided superior cleaning efficacy: